Process for hardening high-speed steel



Patented Oct. 15, 19 29 UNITED-STATES wmnn s'ramirnn, or zunion,SWITZERLAND, ASSIGNOR TO THE FIRM AKTIEN- GEsEL som'r mm uascnmnxranmxnxnsonnn WYSS & cm, or zumcn,

SWITZERLAND PATIENT OFFICE" T rnocnss For; HABDENING nxGn-srnnnsrnar.

No Drawing Application aieanpni 7, 1928, Serial no. 268,375, and inSwitzerland April 23, 1927'.

steel is heated after hardening in an ordinary open forge fire or in anykind of furnace, a soft zone of greater or less thickness is produced,by decarboni'zation, and has to heremoved by grinding it off. Thisphenomenon, which is the cause of severe wear in highspeed steels,appears in aparticularly inconvenient form in the case of shaped pieces,complicated part-s, and'articles which, after hardening, have to bereduced to exact dimensions by grinding and must, besides possess thehighest possible degree of superficial hardness.

Hitherto the procedure' in such cases has been to pack the pieces into abox, of sheet iron or a heat resisting alloy, containing wood charcoal,coke breeze or clnders (wrapping.

the articles in paper and thenheating them in a well closed box is alsoa common practice in some places) the whole being then brought tohardening temperature, after which the art1 cles are removed from thebox and quenched.

This method yielded passable results provided the temperature was notraised above 1200? C. Furthermore, meticulous care had to be taken toremove thearticles from the box and quench them as soon as they had Ifthese points Were not attended to and if the temperature were'increasedor the time of heating prolonged the marginal zones rapidly becamecarbonized and melted off as the meltingpoint of the metal was therebyreduced far below the temperature most suitable for hardening. Underthese conditions the corners and edges of the articles were inevitablydamaged.

Such a steel would,,in the, hardening shops,

be described'as overcooked, and it was generally supposed that in suchcases, the hardening temperature had been pushed to too high a limit.The disadvantages cannot, moreover, be prevented by heating the articlesin a cinder bed. The reason is that the cinders contain a certain amountof'unburnt coal so that local carboniz'ation, at least, must still takeplace. If, on the other hand,-the cinder at high temperatures'and becomecaked on to the articles to be'hardened. I

It frequently happens that appreciable melting off is not noticednotwithstanding the 5 fact thatthe outer surface is'more or less heavilycarbonized. I Insuch a steel, owing to its non-homogeneous com osition,severe stresses are set up during ardening and these, in subsequentworking, or even during hardening may give rise to the formation ofcracks and flaking. Furthermore the cutting edge does not maintain itsshape but scales melting point, and since such temperatures are notadmissible when proceeding according, to the methods hitherto known, theuse of so expensive a material entailed merely a useless waste of money.

- The process which forms the subject matter of the present inventionavoids all these dis advantages and makes the hardening of high speedsteel much more independent of the skill of the hardener. Thisnew'process consists in packing the articles to be hardened,

during heating, in at least one carbide in a finely divided form.Carbide in a finely divided form must here be understood to means agranular and powdered carbide.

For example, for the hardening of high speed steel asilicon carbide in agranular form ca'nbe used, whereby the temperature can be, raised to1380 0. without the-piece of steel suffering damage or burning.

When working according to the now process it is possible to attain goodprotection from sintering without any considerable degree ofcorb'onization taking place, as a slight- 10 1 conductors of'heat thecarbides, particularly silicon carbide, conduct heatverywell. Thus 1yreducing atmosphere is formed. Cakin on of the packing material does nottake p ace and the latter can be used over again as many times as may bedesired, so that the consump- .tion of such material is small. If thereducing action of the repeatedl used silicon carbides has fallen offtoo muc a small quantity of a. more easily oxidizable material such asgraphite powder, for example, may be added. Whereas wood charcoal and'cinders are bad it follows that, in carrying out the new process, owingto the uniform and rapid heating through the vessels, a substantialsaving of fuel is effected and a considerably increased output obtained.Furthermore steels hard- I ened by the new process exhibit veryfavourable properties, since in the structure, owing to the short timeof the heating, the transformation of small points of carbide into largecomplexes scarcely takes place at all.

I claim:

A process for hardening high speed steel articles, consisting in packingthe articles to be hardened preliminarily to their heating, in

silicon carbide in a finely divided form, and I in keeping saidarticlespacked therein during heating.

In testimony whereof I have signed my name to this specification.

WERNER STAUFFER.

